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President Barack Obama pauses during a speech at an interfaith vigil for the victims of the Sandy Hook Elementary School shooting on Sunday, Dec. 16, 2012

Updated at 4:31 AM PDT on Monday, Dec 17, 2012

President Barack Obama had strong, stern words for the country Sunday evening at an interfaith vigil for the victims of the Sandy Hook Elementary School massacre and their families.

Obama said that the nation isn't doing enough to protect children and that "we will have to change."

PHOTOS: Newtown School Shooting

"Caring for our children; it's our first job. If we don't get that right, we don't get anything right," Obama said in front of about 1,000 people in the Newtown High School auditorium. "That is how, as a society, we will be judged. And by that measure, can we truly say as a nation that we're meeting our obligations? Can we honestly say that we're doing enough to keep our children, all of them, safe from harm? ... The answer is no, we're not doing enough. And we'll have to change."

Besides those mourners who packed the auditorium, an overflow crowd of about 1,500 gathered in the school gymnasium. Some waited for hours in a cold drizzle for a chance to grieve with their fellow community members.

Inside the auditorium were a large number of elementary school-age children with their parents. Some of the children were seen squeezing stuffed animals given out by the American Red Cross. Faculty, staff and some students from Sandy Hook Elementary wore green and white ribbons -- the school's colors -- with a small angel in the middle.

"Now more than ever we need each other, because we are all in this together," said Matthew Crebbin, senior minister of the Newtown Congregational Church. "We are in this together."

The president met privately before the vigil with families of the victims and with emergency personnel who responded to the shootings. The White House declined to release details of those meetings.

The grieving in Newtown turned from shock to contemplation Sunday, as it grappled with the news of who is gone and learned it could face weeks before its biggest question — Why? — is answered.

But even as the reality of the town's loss set in and police released a trickle of new information about Friday's school massacre, Newtown remained on edge Sunday — particularly after the evacuation of Mass at a church where eight victims were parishioners. After a threat at St. Rose of Lima Church, the facility was searched, and an all-clear was given.

Sunday also raised the possibility that 20-year-old killer Adam Lanza's horrific rampage through Sandy Hook Elementary School could have been much deadlier. When the 20-year-old shot himself in the head, after killing 20 children, six staff members and his own mother, he left behind hundreds of unused bullets, police said Sunday.

Earlier Sunday, a spokesman for the chief medical examiner announced the final two autopsy results in the Friday shooting, confirming that the killer's mother Nancy Lanza, 52, had been killed by multiple shots to her head and that the gunman had killed himself with a gunshot wound to his head.

Those were just a few more of the grim details released in a case investigators said was among the hardest they had ever handled.

Police warned earlier Sunday that it could be weeks before they have a sense of Adam Lanza's motive, as they continue their grueling investigation of his Friday rampage, and cautioned that a glut of misinformation was being spread on social media websites.

"We're using every single resource in order to paint a complete picture of what happened," Connecticut State Police Lt. Paul Vance told reporters.

Friday's shooting left 20 children and 8 adults, including the gunman's mother and the gunman himself, dead and another two people wounded, Vance confirmed Sunday to NBC Connecticut after a press conference.

Police were interviewing those two survivors, Vance said, as well as many other witnesses to the massacre — many of them children.

"We have a great deal of evidence that we're analyzing," Vance said, declining to describe that evidence, and said police were tracing the histories of the gunman's four weapons "back to when they were on the workbench."

As police sift through evidence and witness accounts of Friday's horrific attack, Newtown was still reeling from Saturday's release of the list of the names of the victims — and wondering whether Sandy Hook Elementary School would ever reopen to children again.

Newtown Police Lt. George Simko said it was "too early" to know if the school might ever reopen, but he added, "I'd find it very difficult to do this."

Memorials to victims grew overnight after police released victims' names Saturday afternoon. On a cold and damp Sunday morning, paper bags lit with candles, one for every victim, flickered beneath the local Christmas tree at one end of downtown Sandy Hook.

At the other end of downtown, figures of angels had been posted on a hill on wooden stakes in memory of the 20 child victims of the shooting.

The official list of victims went up on the Connecticut State Police's website Saturday afternoon, and to see it in black and white, with so many names, and with dates of birth as late as 2006, was a stark reminder of what the town of 28,000 had lost.

The news was accompanied by a methodical account from the state's chief medical examiner of how 12 girls, eight boys and six women were gunned down with chilling efficiency — each hit at least twice — by a young man armed with a .223 Bushmaster rifle inside Sandy Hook Elementary School.

Lanza's father released a statement saying his remaining family was "grieving," "heartbroken" and "struggling to make sense of what has transpired."

"Our hearts go out to the families and friends who lost loved ones and to all those who were injured," Peter Lanza wrote. "We are in a state of disbelief and trying to find whatever answers we can. We too are asking why."

As the picture-postcard town in southwestern Connecticut struggled to find its footing, new details emerged about how the attack unfolded.

Lanza apparently shot his way into the school, shattering the front door glass around 9:30 a.m.

Morning announcements were under way, and witnesses remembered hearing screams and gunshots over the PA system.

Others recalled a custodian running down the hall, yelling that there was a gunman.

Teacher Kaitlin Roig described huddling in a bathroom with her 15 first-grade students, trying to assure them that everything would be alright—even though she didn't believe it.

"I'm thinking, 'We're next,'" Roig told ABC News' Diane Sawyer. "And I'm thinking, as a 6-year-old, 7-year-old, what are your thoughts? I'm thinking I almost have to be their parent. So I said to them, I need you to know that I love you all very much, and it's going to be okay, because I thought that was the last thing they were ever going to hear."

The school's principal, Dawn Hochsprung, and school psychologist Mary Sherlach were in a meeting with a parent, other staff members and school therapist Diane Day when the shooting started, Day told The Wall Street Journal. While most people dove under desks, Hochsprung and Sherlach rushed to see if they could help and ran toward the shooter, schools Superintendent Janet Robinson said.

Hochsprung, 47, a mother of five who viewed her school as a model of opportunity and safety, and Sherlach, 56, who was planning her retirement, were both killed.

Another teacher pressed her body against the door to keep Lanza out—and was shot twice in the process, Day said.

Kindergarten teacher Janet Vollmer recalled hearing the attack unfold over the intercom. She told CBS 2 she tried keep her 19 students calm by telling them a custodian was probably on the roof retrieving a soccer ball. Then she and her aides drew the shades and locked the classroom door.

A half hour passed, and finally police arrived to escort them out. On the way, she noticed blood on the floor. "I don't know whether any of them saw that — we kept going," Vollmer said.

Another teacher helped students get out through a window, Robinson said, and one hid the students in the kiln room as the shooter made his way through the school.

Police reportedly had the students hold hands and close their eyes as they were led from the building.

By 11:03 a.m., officers said the school had been evacuated and was secure. They went to the Lanza home and found the gunman's mother dead of a gunshot wound. Despite earlier reports, it did not appear she was a staff member at Sandy Hook Elementary.

Court records showed that Lanza's parents had divorced in 2008 after 17 years of marriage, according to The New York Times, which added that Peter Lanza had moved out of the family's home.

The state's chief medical examiner, H. Wayne Carver, said the case was probably the "worst that I have seen" in his more than 30 years on the job. He performed autopsies of seven of the victims, all of whom had between three and 11 bullet wounds.

Asked whether the victims suffered, Carver said, "not for very long." Asked where on their bodies they were shot, and he said, "all over." Asked how many rounds were fired, he replied, "lots."

The victims were identified by showing relatives pictures of their faces in order to spare them additional grief.

As the investigation continues, state troopers have been assigned to the parents so the information is communicated directly to them, police said.

The release of the names was a dreaded but anxiously awaited moment as the town — and the nation — struggled to absorb the second-deadliest school shooting in American history, second only to the 2007 Virginia Tech shooting that killed 32.

With so many unanswerable questions, Newtowners sought solace amongst each other, flocking to vigils and religious services and building spontaneous memorials to the victims around town.

In downtown Sandy Hook Saturday night, where Church Hill Road and Washington Avenue intersect, candles for each victim flickered beneath the local Christmas tree, while passersby added flowers, votives and two smaller Christmas trees decorated with children's ornaments and topped by angels. They wrote notes to the victims and their families, promising to pray for them and their town. Some brought their young children and struggled to explain what it all meant.

Across the street, in front of an office building, someone had erected a sign made of Christmas lights that read "FAITH," "HOPE" and "LOVE."

Outside Sandy Hook Wine and Liquor, an American flag on poster board was propped on a bench. Owner Mike Kerler and his wife made cards with each of the victims' names and affixed them to the flag.

Kerler, whose four children attended Sandy Hook Elementary, was glad to see the names released, he said, because it will allow the community to step up in support of them, neighbor to neighbor. The victims included a girl who lived across the street from him, he said.

"I'm still searching for something we can do," Kerler said. "We just want to let them know we're thinking about them and we care."